Good day to one and all, hoping all is well in these times. I have a concern that I would like to address, hoping
someone out there can Help, Thanks. I have just completed my 1St rebuild, 91 Toy 22re at 235,000 miles. I had to have had bigger pistons, I
was told by the machinist, due to wear and tear over time. bigger piston was required, from the standard 92.00mm to 92.50mm "+20 oversize
piston and rings. Their is definitely more power, which is nice. Issue is, it is drinking up more gas than expected, not because of speeding, or
going over 60mph. I am just spending more on gas, driving to and from, my norm. I am used to getting 30 miles per gallon. Can someone
elaborate on this issue, thanks.

 

Basically, what has been done to your engine was to make the cylinders larger in volume than they were before. Therefore they can accept a larger volume of fuel/air mixture, which means more "gas" going into each cylinder for every intake stroke, on every piston. You say "There is definitely more power"; the extra fuel being drawn in and burned is the source of that. Since it's drawing in more fuel than before, of course your mileage (miles per gallon or MPG) is going to go down. It would have been great if you let us know what your MPG is now so it could be compared to your original stated 30 MPG before the rebuild. That could tell a lot as to whether your fuel system is working correctly or not. By my (rough) calculations, you've added about 7% more volume to the engine, so a decrease in MPG of about the same amount (about 2 to 3 MPG) or a bit more than that would only make sense. The loss of MPG is translated into more power. I also figure that if everything is working as it should, you should be getting around 25-26 MPG average highway, around town driving will of course be less.

 

Thank you very much for your knowledge 13Swords.On my next refill I mark the mileage then post.